Treatment of cellulosic materials to impart flame resistance thereto

ABSTRACT

Normally flammable cellulosic material rendered flame resistant by the addition thereto of from about 10 and 30 weight percent, based on the weight of cellulosic material, of calcined boron phosphate.

Unite States Patent 11 1 [111 3,837,93 Jones Sept. 24, 1974 [54] TREATMENT OF CELLULOSHC 2,771,379 11/1956 Di Dario 117/140 R MATERIALS 0 MP R FLAME 3,367,863 2/1968 Cooper et a1. 117/138 X 3,371,058 2/1968 Perizzolo 117/138 X RESISTANCE THERETO 3,383,275 5/1968 Croop et a1. 117/169 R [75] Inventor: Gitfin D. Jones, Midland, Mich. 3,438,847 4/1969 Chase 162/159 x [73] Assignee: The Dow Chemical Company,

Mldland Mlch Primary ExaminerWi1liam D. Martin [22] Fi July 21, 1972 Assistant ExaminerThe0dore G. Davis [21] AppL NO; 273 834 Attorney, Agent, or Firm-Ronald G. Bookens [52] 11.5. C1 117/138, 117/137, 117/140 R, 117/143 B,117/144,117/147,117/152 51 1m. (:1 B4411 1/22 [57] ABSTRACT [58] Field of Search.... 117/137, 138, 140 R, 143 B,

117 144 147 52 1395 CF, 1 9 Normally flammable cellulosic material rendered 252 1; 1 2 159 flame resistant by the addition thereto of from about 10 and 30 weight percent, based on the weight of cel- [5 References Cit d lulosic material, of calcined boron phosphate.

UNITED STATES PATENTS 1,885,870 1l/1932 Snyder 117/137 3 Claims, N0 Drawings TREATMENT OF CELLULOSIC MATERIALS TO IMPART FLAME RESISTANCE THERETO BACKGROUND There are many applications for cellulosic materials requiring a fire-retardant treatment. Among such materials may be mentioned textiles made from cotton and from regenerated cellulose, and paper. It is known to use borax, boric acid and phosphates in commercial laundries and institutions as impregnants to make cellulosic fabrics fire resistant. Such materials, however, lose their flame-retarding properties on washing and may be irritating to the skin.

SUMMARY The present invention provides cellulosic materials having significantly enhanced flame resistance by the addition thereto of from about 10 to 30 percent by weight, based on the weight of the cellulosic material, of a calcined boron phosphate.

The invention is particularly suited for the preparation of cellulosic fabrics having significantly enhanced flame resistance, and resistance to loss of flameresisting properties following washing with water, by impregnating such fabrics with from about 10 and 30 percent by weight of calcined boron phosphate. The invention further contemplates flame-resistant cellulosic articles containing calcined boron phosphate further modified to generate acidity upon incineration; and cellulosic articles containing calcined boron phosphate and having additionally applied thereto a polymeric binder material, particularly where such binder material is a normally crystalline vinylidene chloride polymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The normally flammable cellulosic materials which can be rendered significantly more flame resistant according to the present invention, include wood and paper as well as textiles made from paper, cotton and regenerated celluloses such as rayon, and blends thereof. Particularly advantageous results are obtained by treatment of normally flammable nonwoven fabrics prepared from such materials.

The boron phosphate used must be adequately calcined, to make it resistant to water, e.g., repeated water washing of the treated cellulosic materials. In this regard, boron phosphate calcined at a temperature of at least about 400C. and preferably 600-800C. for a period in excess of about 30 minutes, or at l,000C. for 10 minutes or less, is particularly effective. In general, the calcined boron phosphate must be present in amounts of from about l and about 30 percent, based on the weight of cellulosic material, to provide adequate flame resistance. Generally, such calcined boron phosphate should be in particulate form, and preferably smaller than microns, for ease of uniform distribution on the cellulosic substrate.

The calcined boron phosphate may be added to the cellulosic material in any manner conducive to obtaining a uniform distribution of the boron phosphate particles on the cellulosic substrate, e.g., by application of an aqueous suspension of such material to any generally open cellulosic fabric or loosely twisted yam. The calcined boron phosphate may also be added in the beater prior to forming a nonwoven sheet as on a paper machine.

The present invention further contemplates various modifications whereby the calcined boron phosphate is modified to not generate appreciable acidity by mere usage of the impregnated cellulosic material but to generate significant acidity during incineration. Such modifications include: (1) the use of phosphorous, hypo phosphorous acid or P 0 as a partial or complete replacement for phosphoric acid in reacting with boric acid to make boron phosphate, and calcining such material in a substantially oxygen-free atmosphere followed by chlorinating the surface of the product and treatment with ammonia; (2) preparation of a boron amido phosphate either by using a partly amidized phosphoric acid initially (and calcining in an inert atmosphere); (3) mixing carbon with boron phosphate and chlorinating in a substantially oxygen-free atmosphere'followed by treatment with ammonia; and (4) bringing boron phosphate in contact with phosphorus oxychloride or pentachloride in a dry atmosphere, rinsing with an inert solvent, followed by treatment with ammonia.

Especially good results are obtained when treating normally flammable cellulosic textile materials with calcined boron phosphate, by additionally impregnating such textile with a polymeric binder. If the fabric is nonwoven, a binder is necessary to impart strength. The binder is also necessary to retain the boron phosphate. For a nonflammable result, the binder must itself be nonflammable. Representative of preferred such binder materials are the normally crystalline vinylidene chloride polymers.

Typical of such normally crystalline vinylidene chloride polymers are those containing from about to percent by weight of vinylidene chloride with the remainder being composed of one or more monoethylenically unsaturated comonomers exemplary of which are the esters and amides of acrylic acid, methacrylic acid and maleic acid or other copolymerizable vinyl acids. Specific esters are those which contain alcohols of 1-8 carbon atoms, such as methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl methacrylate, octyl acrylate, 2-ethylhexyl acrylate, etc. Specific amides include acrylamide, methacrylamide, tbutylacrylamide and primary alkyl acrylamides such as N,N-dimethylacrylamide and the like. Other monomers which may be copolymerized with vinylidene chloride include vinyl chloride, acrylonitrile, methacrylonitrile and acrylates or methacrylates of glycols, e. g., hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate.

Preferably, such normally crystalline vinylidene chloride polymer is in latex form when added to the cellulosic material, and particularly a latex which is adequately buffered to prevent tenderizing of such cellulosic material. When so used the polymer must be noncrystalline and film forming at the time of application.

Exemplary of other useful polymeric binders are the water-soluble phosphorylated polymers, e.g., as described in the Japanese Pat. No. 46-7704.

It has been found to be undesirable to pre-mix the polymeric binder material and the calcined boron phosphate prior to addition thereof to the cellulosic material, as the binder material tends to coat the boron phosphate particles thus preventing an intimate dispersion of such particles on the cellulose substrate. It is essential that the calcined boron phosphate come in contact with, and form a uniform protective char on, the cellulosic substrate during exposure to flame.

When using a polymeric binder material, such material is generally employed in amounts of from about 10 to about 20 percent, based on the weight of the cellulosic material, with at least one part by weight of binder being present per two parts by weight of calcined boron phosphate.

The following nonlimiting examples, wherein all parts and percentages are by weight, illustrate the present invention:

EXAMPLE l In each of a series of experiments, individual portions of a nonwoven rayon fabric (anisotropic Diana cloth) were treated with varying amounts of calcined boron phosphate and varying amounts and types of polymeric binders and the flammability of such fabric determined, using the following procedures:

A. Application of Additives to the Fabric Boron phosphate (B1 calcined at a temperature of about 1,000C. is applied from a 3 to 4 percent aqueous suspension. The BPO is screened through a 50 mesh sieve prior to use. The cloth, supported on a supporting screen, is immersed into the suspension until saturated and then removed. Excess liquid is rolled out of the fabric before drying for minutes at 8590C.

Binder is then applied from a l to 2 percent aqueous solution or suspension byspraying it on the cloth after BPO, application. The cloth is then dried again at 8590C. for 10 minutes.

B. Flammability Test In order to screen various binders a burn down" technique was used, having been found effective in differentiating flammability characteristics of various samples. A burn-up technique does not differentiate.

The effective sample size for testing is I inch by 6 or 7 inches. The sample is vertically suspended from a frame made of aluminum foil which hangs inside a glass chimney 40 cm. long and of 80 mm. diameter. Use of the chimney reduces room air current effects.

Test sheets are considered self-extinguishing according to the following system:

Excellent self-extinguishes immediately upon removal of flame source.

Good self-extinguishes after having burned down no more than 1 cm. after removal of flame source.

Acceptable self-extinguishes after having burned down no more than 2 cm. after removal of flame source.

C. Polymeric Latex Binders Used A. An interpolymer of 80 percent vinylidene chloride, percent butyl acrylate, 5 percent acrylonitrile containing 1.6 percent sulfoethyl methacrylate.

B. An interpolymer of about 92 percent vinylidene chloride, 8 percent acrylonitrile and 1.45 percent sulfoethyl methacrylate.

C. An interpolymer of about 86 percent vinylidene chloride, 10 percent methyl methacrylate, 4 percent methyl acrylate and 1.2 percent sulfoethyl methacrylate.

D. An interpolymer of 50 percent vinylidene chloride, 47 percent butadiene, 2 percent methacrylic acid and 1 percent acrylonitrile.

E. A partially hydrolyzed polyvinyl chloroacetatetrimethyi phosphite derivative.

F. A copolymer of 65 percent vinylidene chloride and 35 percent vinyl dimethoxyphosphinylacetate.

G. A phosphorylated chlorinated polyethylene.

The following Table 1 sets forth the amounts of calcined boron phosphate and the amounts and types of polymeric binders used, and the flammability results obtained. The particular boron phosphate used was characterized by having a 2 percent weight loss upon heating to 1,000C.

TABLE I Calcined Boron Flammability Exp. Phosphate Polymeric Binder Test No. (Wt. 72) (Type) (Wt. 92) Results 1 None None Burned down completely 2 9.4 None Good 3 None (A) 17.1 Burned down completely 4 9.1 (A) 3.5 Acceptable 5 12 (B) 7 Good 6 13.4 (C) 3.5 Acceptable 7 None (C) 16.7 Burned down completely 8 13.7 (D) 3.7 Good 9 None (D) ll.l Burned down compl'eteiy l0 16 (E) 4 Good ll None (E) 9 Burned down completely l2 15 (F) 13 Excellent 13 None [Fl 13 Burned down completely 14 15 (G) 37 Excellent 15 None (G) 15 Burned down completely By way of further comparison, similar experiments were conducted using from about 15 to 18 percent by weight of a dispersible alumina as the flameprooflng material. Each of such tests resulted in the cloth burning down completely.

EXAMPLE 2 In each of a series of experiments individual portions of a nonwoven rayon fabric (as described in Example 1) were separately treated with the calcined boron phosphate of Example 1 wherein such boron phosphate was further modified as follows:

Experiment No. Modification l6 BPO, passed through plasma at 400 amp. 32 volts.

I7 BPO, mixed with carbon, chlorinated at 700C. and reacted with ammonia gas.

BPO, reacted with ammonia gas at l9 BPO, reacted with POCl in Cruel,

and then ammonia gas at room temperature.

20 As per 19 but ammonia gas reaction at C.

21 Bro. mixed with 4 MgCO Mg(OH),-4H,O

in 4:3 weight ratio.

Each treated sample was then tested for flammability as per the technique set forth in Example 1. The following Table ll sets forth the experiment number, the pH of the modified BPO the amount of modified BPO added onto the fabric and the flammability of the impregnated fabric.

TABLE II Burn Exp. No. pl-l Add on. 7c Distance, cm.

16 3.5 l4 l0, 6. 4 17 645 20 3, 7 18 45 21 3 19 2.25 23 l, 2 2O 3 4 l3 1 2l l8 4 6 sequential steps of l impregnating said cellulosic fabric with from about 10 to about 30 percent by weight of a boron phosphate based on the weight of the cellulosic fabric which has been calcined at a temperature of at least about 400C for a period greater than 30 minutes or at a temperature of about 1,000C for a period of about 10 minutes or less, then (2) applying a polymeric binder to the impregnated cellulosic fabric, said binder being in the form of a film-forming latex when added to said cellulosic fabric said polymeric binder being present in amounts of from about 10 to about 20 percent based on the weight of cellulosic fabric with at least one part by weight of binder being present per two parts by weight of calcined boron phosphate and (3) drying the impregnated cellulosic fabric.

chloride polymer. 

2. The process of claim 1 wherein the calcined boron phosphate is treated prior to application to said cellulosic fabric to render said calcined boron phosphate capable of generating acidity when incinerated.
 3. The process of claim 1 wherein said polymeric binder material is a normally crystalline vinylidene chloride polymer. 